Apparatus and method for controlling the level of oil in a surge drum

ABSTRACT

APPARATUS CONTROLS THE LEVEL OF OIL IN A SURGE TANK IN A PROCESSING UNIT OF A REFINING SYSTEM, RECEIVING A CHARGE LIQUID AND WHICH IN TURN PROVIDES A CHARGE LIQUID TO A SECOND PROCESSING UNIT OF THE REFINING SYSTEM. A SIGNAL IS PROVIDED CORRESPONDING TO A DESIRED CHANGE &gt;FR TO BE MADE IN THE FLOW RATE OF THE SECOND PROCESSING UNIT CHARGE LIQUID. A FIRST CHANGE NETWORK RECEIVING THE CHANGE SIGNAL DETERMINES THE MAGNITUDE OF THE DESIRED CHANGE TO THE SECOND PROCESSING UNIT CHARGE LIQUID FLOW RATE AND PROVIDES A FLOW RATE SIGNAL FOR CONTROLLING THE FIRST PROCESSING UNIT CHARGE LIQUID FLOW RATE IN ACCORDANCE WITH THE DESIRED CHANGE SIGNAL. THE CHANGE &gt;FH IN THE FIRST PROCSESSING UNIT CHARGE LIQUID FLOW RATE MAY BE EQUAL TO OR SOME PORTION OF THE CHANGE &gt;FR TO BE MADE IN THE SECOND PROCESSING UNIT LIQUID FLOW RATE DEPENDING ON THE MAAGNNITUDE OF THE CHANGE SIGNAL. THE CHANGE &gt;FH DIFFERES IN DIFFERENT PROPORTIONS DEPENDING ON THE MAGNITUDE OF THE CHANGE &gt;FR. THE NETWORK INCLUDES AN ABSOLUTE VALUE CIRCUIT WHICH PROVIDES A SIGNAL CORRESPONDING TO THE MAGNITUDE OF THE CHANGE SIGNAL. THE CHANGE IN THE SECOND PROCESSING UNIT CHARGE LIQUID FLOW RATE IS DELAYED FOR A PREDETERMINED TIME INTERVAL AND THEN IMPLEMENTED. THE DURATION OF THE TIME INTERVAL IS ALSO DETERMINED AS A FUNCTION OF THE MAGNITUDE OF THE CHANGE &gt;FR.

Aug. 13, 1974 Filed Dec. 30, 1971 w. L. HOPKINS ETAL v APPARATUS ANDMETHOD FOR CONTROLLING THE LEVEL OF OIL IN A SURGE DRUM 2 Sheets-Sheet 150 'HYDRO-TREATER REACTOR FLOW F I I RECORDER CONTROLLER GAS CHARGE OIL28 P STRIPPER TOWER L 'l/E o FLOW RECORDER REFORMER CONTROLLER REACTORS4 E62 I sTEAM)F 6| LEvEL A CONTROLLER E HYDRO- 43 m2? NETWORK NETWORK t2 5 5 SOURCES OF D.C. V2- v VOLTAGES W. L. HOPKINS ETAL AND Aug. 13,1974 APPARATUS METHOD FOR CONTROLLING THE LEVEL OF OIL IN A SURGE DRUM 2Sheets-Sheet 2 FEEDBACK CIRCUIT m In XA. :w m mm C. 5 NI 1 J a A E U m wm 4 m m m e :m X m w -:A C C mtllw E |I|%I. I I I I I I III -IIIIII v vv V V HYDROTREATER CHANG E NETWORK I I I l I I I J Dnv W 60 T )..wm E m0 G E 00 00% F Q v N R l 6 M H w! E 0 m C w 0 w E R 5 I m m z 5 n )w n mNH K P P 0c C O mw mm m Q FF FF L E V. 3 w 0 I mb OH s 9 0 m ww 2 Dm BIR I l I I I I I I II II I I I I 11;] E5 V| V9 United States Patent 01hoe 3,829,375 Patented Aug. 13, 1974 Int. Cl. Clog 23/00 US. Cl. 208-899 Claims ABSTRACT OF THE DISCLOSURE Apparatus controls the level of oilin a surge tank in a processing unit of a refining system, receiving acharge liquid and which in turn provides a charge liquid to a secondprocessing unit of the refining system. A signal is providedcorresponding to a desired change AF to be made in the flow rate of thesecond processing unit charge liquid. A first change network receivingthe change signal determines the magnitude of the desired change to thesecond processing unit charge liquid flow rate and provides a flow ratesignal for controlling the first processing unit charge liquid flow ratein accordance with the desired change signal. The change AF in the firstprocessing unit charge liquid flow rate may be equal to or some portionof the change AF to be made in the second processing unit liquid flowrate depending on the magnitude of the change signal. The change AFdiffers in different proportions depending on the magnitude of thechange AF The network includes an absolute value circuit which providesa signal corresponding to the magnitude of the change signal. The changein the second processing unit charge liquid fiow rate is delayed for apredetermined time interval and then implemented. The duration of thetime interval is also determined as a function of the magnitude of thechange AF BACKGROUND OF THE INVENTION The present invention relates tocontrol systems in general and, more particularly, to a control systemfor controlling a level of a liquid in a surge drum.

DESCRIPTION OF THE PRIOR ART Heretofore liquid level control for a surgedrum in a processing unit was accomplished by sensing the liquid levelin the surge drum and manually controlling the liquid being provided bythe processing unit to a second processing unit. However, when a largechange is made in the liquid flow rate going to the second processingunit, the change either completely evacuates the surge drum resulting ina starving of the second processing unit or causes an undesirable highliquid level in the surge drum thereby reducing its surge capacity.

The system of the present invention determines the change that shall bemade in the flow rate of a liquid entering the first processing unit inview of an anticipated change to be made in the flow rate of the liquidgoing from the first processing unit to the second processing unit andinitiates the change to the first processing unit charge liquid flowrate. The system also determines the time lag for the effect of thechange in the first processing unit charge liquid flow rate on the surgedrum liquid level.

SUMMARY OF THE INVENTION Apparatus controls the level of a first liquidin a surge drum of a system processing a second liquid. The systemreceives the second liquid and discharges the first liquid afterprocessing. The apparatus includes a source providing a signalcorresponding to a change to be made to the flow rate of one of theliquids. Equipment receiving the change signal changes the flow rate ofthe other liquid in accordance with the change signal. Other equipmentreceiving the change signal changes the flow rate of the one liquid atsome predetermined time relative to the change in the other liquid flowrate in accordance with the change signal.

The objects and advantages of the invention will appear hereinafter froma consideration of the detailed description which follows, takentogether with the accompanying drawings wherein one embodiment of theinvention is illustrated by way of example. It is to be expresslyunderstood, however, that the drawings are for illustration purposesonly and are not to be construed as defining the limits of theinvention.

DESCRIPTION OF THE DRAWINGS FIG. 1 shows a control system, constructedin accordance with the present invention for controlling the oil levelin a surge drum in a hydrotreater unit, which is also partially shown inschematic form, providing oil to a catalytic reforming unit.

FIGS. 2 and 3 are detailed block diagrams of the hydrotreater changenetwork and the reformer change network, respectively, shown in FIG. 1.

DESCRIPTION OF THE INVENTION Referring to FIG. 1, there is shown aportion of a hydrotreater unit in which charge oil is processed toprovide an output for further processing in a catalytic reforming unit.It is not necessary to the understanding of the present invention toknow the details of the hydrotreating process involved and hence theprocess will only be briefly described. Hydrogen in line 3 mixes withcharge oil entering a hydrotreater reactor 1 through lines 2, 3.Eflluent from reactor 1 leaves by way of line 7 and enters a flash drum9. Flash drum 9 provides a. gaseous fraction to a separator 14 by way ofa line 15. Separator 14 further processes the gaseous fraction in line15 to provide a gas output through a line 22 and a liquid to line 20 forfurther processing in stripper tower 2.1.

Stripper tower 21 provides a gas output through line 28, while the oilfrom stripper tower 21 is withdrawn by a pump 29 through a line 30. Pump29 provides the oil as charge oil to a catalytic reformer reactor (notshown) through a line 33. Minor transient changes in the flow rate ofthe charge oil in line 33 are prevented from affecting the hydrotreatercharge rate by use of a surge drum 35 receiving charge oil for thecatalytic reforming unit from stripper tower 21 through a line 36 andproviding it to line 30 through a line 37.

The flow rate of the charge oil in line 33 is held at a specific valuebecause it is a primary process variable and is often referred to asspace velocity. Since the catalytic reformer charge rate is heldrelatively constant, it is varied to adjust for variation in the reactorcharge surge drum level.

The adjustments for variation in surge drum 35 oil level is made bycontrolling the flow rate of the charge oil in line 2 to thehydrotreater unit. When a substantial change is made to the flow rate ofthe charge oil in line 33, it is desirable that the flow rate of thecharge oil in line 2 be changed accordingly and at some time prior tothe change in flow rate of the charge oil in line 33, so that surge drum35 is not completely evacuated by the change or completely filled up bythe change.

Due to physical properties of the hydrotreater unit, the change AF inflow rate of the charge oil in line 2 is some proportion of the changeAF in flow rate of the charge oil in line 33 as indicated in thefollowing equation:

H= (AFR) Time Absolute value of delay AFR (in b.p.h.) Factor K (minutes)AFR 1. 2031 11560 0.85 7 AFn 60 0. 75 9 A hydrotreater change networkprovides signals E corresponding to a target hydrotreater flow rate Ethrough E, in accordance with direct current voltages V through V from asource 41. Signals E through E; are applied to a reformer change network42 receiving direct current voltages V and V from source 41, which inturn provides a signal E corresponding to the desired flow rate for thecharge oil in line 33. The change in signal E will occur at somepredetermined time after a change in signal E as hereinafter explained.

Signal E from hydrotreater change network 40 is applied to summing means45 receiving a signal E from a level controller 48. A sensor 49connected to surge drum 35 senses the level of the oil in surge drum 35and provides a corresponding signal E to controller 48. Controller 48provides signal E7 corresponding to the difference between the actualoil level in surge drum 35 and the desired level as represented by theposition of the set point in controller 48. The adjustment of the setpoint in controller 48 may be done manually and is not part of thiscontrol system.

If the oil level in surge drum 35 decreases, signal B, will increase ina positive direction. Signal 7 is added to signal E by summing means 45to provide signal E to a flow recorder controller 50. Signal E adjuststhe set point of flow recorder controller 50. Flow recorder controller50 receives a signal from a conventional type flow sensor correspondingto the flow rate of the charge oil in line 2. A valve56 is controlled byan output from flow recorder controller 50 to control the flow rate inline 2 in accordance with the position of controller 50 set point. Thus,signal E is increased by the positive signal E to change controller 50set point for increased flow. Controller 50 controls valve 56 toincrease the flow rate of the charge oil in line 22 and hence toincrease the charge rate of reactor 1. Eventually, the increased flowrate in line 2 causes an increase in the oil level in surge drum 35.

The opposite is true when the oil in surge drum 35 increases above itspredetermined level. Level controller 48 provides a negative signal E inresponse to signal E; which in effect decreases signal E Flow recordercontroller 50 set is changed by signal E to decrease the flow rate inline 2 thereby eventually restoring the oil in surge drum 35 to itspredetermined value.

The flow rate of the charge oil in line 33 is controlled by controllingthe speed of pump 29. Pump 29 is mechanically driven by a turbine 60receiving steam through a line 61. A valve 63 in line 61 controls steamin line 61 to control the speed of turbine 60 and hence the speed ofpump 29. A flow recorder controller 65 has a set point positioned inaccordance with signal E and receives a signal corresponding to the flowrate of the charge oil in line 33 from a flow rate sensor 66 in line 33.Controller 65 provides a signal to operate valve 63 so that the flowrate of the oil in line 33 is in accordance With the set point position.Thus, the flow rate in line 33 may be adjusted by adjusting the setpoint of flow recorder controller 65 thereby adjusting the speed of pump29.

Referring to FIGS. 1 and 2, an operator initiates the change of thereformer charge rate by adjusting the amplitude of voltage V Voltage Vcorresponds to the change AF to beimpressed on the flow rate of the oilin line 33 and as such may be positive for an increase in charge rate ornegative for a decrease in the charge rate. An absolute value circuit72. comprising multipliers 73 and 74, logarithmic amplifier 75,operational amplifier 76 and a feedback circuit 77 provide signal Ecorresponding to the absolute value of voltage V The absolute value isobtained by squaring voltage V, and taking the square root of thesquared voltage. Multiplier 73 eifectively squares voltage V Logarithmicamplifier 75 provides a signal corresponding to the logarithm of theoutput from multiplier 73 to multiplier 74. Multiplier 74 multiplies theoutput from logarithmic amplifier 75 with voltage V corresponding to avalue of 0.5. The product signal from multiplier 74 is applied tooperational amplifier 76 having feedback circuit 77 connected across itsinput and output. Feedback circuit 77 is a function generator which maybe of the type manufactured by Electronic Associates as their partnumber PC-l2. Operational amplifier 76, in conjunction with feedbackcircuit '77, provides a signal corresponding to the antilog of theproduct signal from multiplier 74 as signal E Comparators 80, 81 controlwhich correlation factor K will be used in charging the flow rate of thecharge oil in line 2. Comparators 80, 81 compare singal F with voltagesV and V; respectively. Voltage V, is more positive than voltage V Forthe condition Where AF is less than 20 b.p.h., signal E is more negativethan voltages V V causing comparators 80, 81 to provide signals E and Erespectively at a high level and a low level respectively. Signals E Erender electronic switches 84 and 84A, respectively, conductive andnon-conductive respectively. Signals E B are inverted by inverters 90and 91, respectively, and applied to an AND gate 92. The inverted signalE from comparator disables AND gate 92 causing AND gate 92 to providesignal E, at a low level. Signal E renders an electronic switch 84Bnonconductive. Switch 84 passes voltage V corresponding to a correlationfactor of 1.00, While switches 84A, 84B block voltages V and Vrespectively, corresponding to correlation factors of 0.75 and 0.85respectively.

A multiplier 85 multiplies the change AF voltage V by voltage V.,,passed by switch 84 to provide signal E corresponding to the change AFto be impressed on the hydrotreater charge rate. Summing means 88 sumssignal E from multiplier 85 with a direct current voltage Vcorresponding to a target flow rate for the charge oil in line 2 toprovide signal E to flow recorder controller 50.

For the condition Where AF is equal to or greater than 20 b.p.h. andequal to or less than 60 b.p.h., signals E E from comparators 80 and 81,respectively, are at low levels since signal E is equal to or morepositive than voltage V but less positive than voltage V Low lovelsignals E E render switches 84 and 84A respectively non-conductive toblock voltages V and V respectively. Inverters 90, 91 invert outputs Eand E respectively, to high levels which enables AND gate 92. Whenenabled, AND gate 92 provides signal E, at a high level to render switch84B conductive to pass voltage V, to multiplier 85. The development ofsignal E is the same as heretofore described except voltage V; is nowused in lieu of voltage V For the condition where AF is greater than 60b.p.h., voltage V is used in developing signal E Signal E is morepositive than voltages V V causing comparators 80, 81 to provide signalsE and E respectively, at a low level and a high level, respectively.Since signal E is at a high level, AND gate 92 provides signal E at alow level in response to the inverted signal E from inverter 91. SignalE renders switch 84A conductive to pass voltage V to multiplier 85 whilesignals E E render switches 84 and 8413, respectively, non-conductive toblock voltages V and V respectively, Voltage V is used in same manner indeveloping signal E as heretofore described for voltage V As notedpreviously in the table, there is associated a time delay with thechange to the flow rate of the charge oil in line 33, to allow thechange in line 2 charge oil to affect the level of oil in surge drum 35.Referring to FIGS. 1, 2 and 3, the absolute value signal E isdifferentiated by a conventional type differentiating circuit 99.Differentiating circuit 99 provides a positive spike pulse which isinverted by an inverter 100 so that it may trigger a one shotmultivibrator 101 causing multivibrator 101 to provide a positive pulse.The spike pulse differentiating circuit 99 resets a flip-flop 103 to aclear state. The positive pulse from multivibrator 101 resets a counter104 while the trailing edge of the puositive pulse triggers a flip-flop105 to a set state. Flip-flop 103 or 105 provides a high level directcurrent output while in a set state, and a low level direct currentoutput while in a clear state. The high level output from flip-flop 105enables an AND gate 106 to pass timing pulses from a clock 110 tocounter 104. The pulse repetition rate of the timing pulses from clock110 should be selected to allow counter 104 to exceed the maximum timedelay shown in the table without recycling. Counter 104 counts thetiming pulses. A logic decorder 111 includes AND gates connected tocounter 104 in a manner so as to provide three high level output signalsE 1, E and E in response to different counts in counter 104 which occurat different times.

AND gates 112, 112A and 112B receive signals E E and 23, respectively,from decoder 111 and signals E E and E respectively, hydrotreater changenetwork 40. AND gates 112 through 112B control the selection of theproper time delay associated with AF When AF is less than 20 b.p.h., Eis at a high level, as heretofore explained, and enables AND gate 112.Signal E from logic decorder 111 is at a low level until the count incounter 104 corresponds to the time delay which, by way of example, maybe five minutes. When the count in counter 104 corresponds to fiveminutes, signal E goes to a high level and passes through the enabledAND gate '1|12 and an OR gate 114 to trigger flip-flop 105 to a clearstate. AND gate 106 is disabled by the low level output from flip-flop105 and blocks the timing pulses from clock 110 to prevent furthercounting by counter 104 so that output E remains at a high level.

Signal E passed by OR gate 114 is inverted by an inverter 115 to triggerflip-flop 103 to a set state. The high level output from flip-flop 103renders an electronic switch 120 conductive to pass the AF changevoltage V to summing means 1121. Summing means 121 sums the passedvoltage V with voltage V which corresponds to the target reformer chargerate, to provide signal E to fiow recorder controller 65 after the timedelay of five minutes. Before electronic switch 120 was renderedconductive summing means 121 provided voltage V as signal E When signalE is a high level signal, then signals E E are low level signals andonly AND gate 112A is enabled. When counter 104 provides signal E signalE is blocked by the disabled AND gate 112 and counter 104 continues tocount. When the count is counter 104 corresponds toseven minutes, signalE goes to a high level and passes through AND gate 112A to have the sameresults as described heretofore for signal E passing through AND gate112 for a time delay of five minutes.

When signal E is at a high level, signals E E have no effect on the timedelay since AND gates 112, 112A are disabled by signals E and Erespectively being at low levels. Counter 104 keeps on counting past thefive and seven minute time intervals until its count corresponds to thetime delay associated with the condition AF 6O b.p.h., which, forpurpose of illustration, may be nine minutes; when the count in counter104 corresponds to nine minutes signal E goes to a high level and passesthrough AND gate 112B, which is enabled by signal E and OR gate 114 withthe same effect as heretofore described when signal E passed through ORgate 114. However, now signal E does not include voltage V until after atime delay of nine minutes instead of five minutes.

Flip-flop 103 permits a second change to be made to the catalyticreforming unit charge flow rate after the appropriate time delay. If theoutput from OR gate 114 controlled switch directly, any change AF madeafter a first change AF would instantaneously change signal E and effectthe catalytic reforming unit charge oil flow rate. However, withflip-flop 103, a second change AF resets flip-flop 120 to a clear stateto render switch 120 non-conductive. Switch 120 is not renderedconductive again until the appropriate time delay so that the new levelvoltage V does not instantaneously affect signal E The amount of timethat signal E will then correspond to voltage V is negligible withregard to the refining unit response time.

It is obvious from the aforementioned equation that a change AF in thecharge oil flow rate in line 2 may be predetermined instead of a AF andthat the change AF of the charge oil flow rate in line 33 would bedependent on the change AP 01 The correlation factor K has the samevalues as heretofore mentioned. The change AF would be initiated firstand, after the proper time delay, the change AF would be initiated.

The apparatus of the present invention as heretofore described controlsthe level of a liquid in a surge drum to avoid substantial changes inthe liquids level due to process changes in a system incorporating thesurge drum. The apparatus as heretofore described changes the flow rateof charge oil entering a hydrotreater unit, having a surge drum andproviding charge oil to a catalytic reforming unit, at some time pior toa change being made in the catalytic reforming unit charge oil flow rateso that by the time the catalytic reformer charge oil flow rate changereaches the surge drum the effect of the hydrotreater charge oil flowrate change also reaches the surge drum. The effect of the catalyticreforming unit charge oil flow rate change on the surge drum oil levelis thereby minimized. The apparatus also determines the magni tude ofthe catalytic reforming unit charge oil change and uses the determinedmagnitude to control the hydrotreater charge oil flow rate change.

What is claimed is:

1. A method for controlling the level of a hydrotreated oil liquid in asurge drum of a system processing a charge oil liquid and dischargingthe hydrotreated oil liquid, said system including a hydrotreater unitfor receiving said charge oil liquid and a surge drumfor receiving someof said hydrotreated oil liquid and providing some of the hydrotreatedoil liquid being discharged from the system, said method comprising thesteps:

(1) selecting a value of a correlation factor K from a group ofpredetermined values in accordance with the magnitude of a predeterminedchange AF to be made to the flow rate of said charge oil liquid,

(2) changing the flow rate of said charge oil liquid by the amount APand I (3) changing the flow rate of said hydrotreated oil liquid beingdischarged from the system upon the completion of a time intervalbetween the changing AF K 2 said time interval being determined inaccordance with the magnitude of the predetermined change AFB.

2. A method as described in claim 1 which further comprises the stepproviding said discharged hydrotreated oil liquid to a catalyticreforming unit.

3. A method for controlling the level of a hydrotreated oil liquid in asurge drum of a system processing a charge oil liquid and dischargingthe hydrotreated oil liquid, said system including a hydrotreater unitfor receiving said charge oil liquid and a surge drum for receiving someof the hydrotreated oil liquid and providing some of the hydrotreatedoil liquid being discharged from the system, said method comprises thesteps:

(1) selecting a value of a correlation factor K from a group ofpredetermined values in accordance with the magnitude of a predeterminedchange AF to be made to the flow rate of said hydrotreated oil liquidbeing discharged from the system,

(2) changing the flow rate of said charge oil liquid by the amount AF inaccordance with the following equation:

, and

(3) changing the flow rate of said hydrotreated oil liquid beingdischarged from the system by the amount AF upon the completion of atime interval after the changing of said charge oil liquid flow rate,said time interval being deter-mined in accord ance with the magnitudeof the predetermined change AP 4. A method as described in claim 3 whichfurther comprises the step:

providing said discharged hydrotreated oil liquid to a catalyticreforming unit.

5. Apparatus for controlling the level of a hydrotreated oil liquid in asurge drum of a system processing a charge oil liquid and dischargingthe hydrotreated oil liquid, said system including a hydrotreater unitfor receiving said charge oil liquid and a surge drum for receiving someof said hydrotreated oil liquid and providing some of the hydrotreatedoil liquid being discharged from the system, said apparatus comprising:

(1) change signal means for providing a change signal corresponding to apredetermined change AF to be made to the flow rate of the hydrotreatedoil liquid being discharged from the system,

(2) charge oil liquid change means connected to said change signal meansfor changing the flow rate of charge oil liquid to said hydrotreaterunit by the amount AF in accordance with the change signal and thefollowing equation:

where K is a correlation factor, and

(3) hydrotreated oil liquid change means connected to said change signalmeans for changing the flow rate of said hydrotreated oil liquid beingdischarged from the system by the amount AF upon the completion of atime interval between the flow rate changes provided by the AF changemeans and the AF change means, said time interval being determined inaccordance with the magnitude of the predetermined change AP 6.Apparatus as described in Claim 5 in which K has different valuesassociated with difierent magnitudes of AF and said charge oil liquidchange means includes means connected to the AF change signal means forproviding a signal corresponding to an absolute value of AF inaccordance with the AF change signal, means connected to the AF changesignal means and to the absolute value signal means and receiving directcurrent voltages corresponding to ditferent values of K for providing aAF change signal in accordance with the AF change signal, the absolutevalue signal and the received direct current voltages, means for sensingsaid hydrotreated oil liquid level in the surge drum and providing asignal corresponding to the difference between the sensed oil level anda predetermined oil level, means connected to the AF change signal meansand t0 the oil level sensing means and receiving a direct currentvoltage corresponding to a predetermined flow rate for the hydrotreatercharge oil for changing the hydrotreater charge oil flow rate inaccordance with the AF change signal, the ditference signal from oillevel sensing means and the last mentioned direct current voltage.

7. Apparatus as described in Claim 6 in which said hydrotreated oilliquid change means includes means connected to the AF change signalmeans for delaying the AF change signal, and means connected to thedelaying means for changing the flow rate of said hydrotreated oilliquid in accordance with the delayed AF change signal so that thechange in the flow rate of said hydrotreated oil liquid occurs at apredetermined time relative to the change in the flow rate of saidcharge oil liquid.

8. Apparatus for controlling the level of a hydrotreated oil liquid in asurge drum of a system processing a charge oil liquid in a hydrotreaterand discharging the hydrotreated oil liquid, said system including ahydrotreater unit for receiving said charge oil liquid and a surge drumfor receiving some of said hydrotreated oil liquid and providing some ofthe hydrotreated oil liquid being discharged by the system, saidapparatus comprising:

(1) change signal means for providing a change signal corresponding to apredetermined change AF to be made to the flow rate of the said chargeoil liquid flow rate;

(2) charge oil liquid change means connected to said change signal meansfor changing the flow rate of said charge oil liquid by the amount AF inaccordance with the change signal, and

(3) hydrotreated oil liquid change means connected to the change signalmeans for changing the flow rate of the hydrotreated oil liquid beingdischarged from the system by the amount AF at some time after thechanging of the charge oil liquid flow rate in accordance with thechange signal and the following equation:

where K is a correlation factor, the time interval between the changingof the flow rates being determined in accordance with the magnitude ofthe predetermined change AF 9. Apparatus as described in Claim 8 inwhich K has different values associated with ditferent magnitudes of AFand said hydrotreated oil liquid change means includes means connectedto the AF change signal means for providing a signal corresponding to anabsolute value of AF in accordance with the AF change signal, meansconnected to the AF change signal means and to the absolute value signalmeans and receiving direct current voltages corresponding to difierentvalues of K for providing a AF change signal in accordance with the AFchange signal, the absolute value signal and the received direct currentvoltages, means connected to the AF change signal means and to theabsolute value signal means for delaying the AF change signal for a timeinterval, so that the change to the flow rate of said bydrotreated oilliquid is made at a predetermined time relative to the change in theflow rate of said charge oil liquid, the duration of the time intervalbeing determined in accordance with the absolute value signal, and meansreceiving the delayed AF change signal from the delay 3,365,393 1/1968Wooten 208-212 means and receiving a direct current voltage correspond-3,066,093 11/1962 Ruef et a1 208212 ing to a predetermined flow rate ofsaid hydrotreated oil 3,309,420 3/ 1967 Van 'Pool 2606835 8 liquid forcontrolling flow rate of said hydrotreated oil 3,365,393 1/1968 Wooten208-212 provided to said catalytic reforming unit in accordance3,720,730 3/1973 Hopkins et al. 260683.58 with the delayed AF changesignal and the received di- 5 eet current voltage. DELBERT 'E. GANTZ,Primary Examiner References Cited G. J. CRASANAKIS, Assistant ExaminerUNITED STATES PATENTS 10 US. Cl. X.R.

2,998,016 8/1961 Bottenberg et a1 1378 20860, 209, DIG. 001; 137-2;235150.1, 151.12 3,273,576 9/1966 Fluegel et al. 1372 y UNITED STATESPATENT OFFICE CERTIFICATE OF CORRECTION Patent: No. 3 29,376 DatedAugust 13, 19?

Inventor) W.L. Hopkins, L.A. Chvatal, W.D. White It is certified thaterror appears in the above-identified patent and that said LettersPatent are hereby corrected as shown below:

' Co1.l, line 62 After "unit charge liquid flow rate" insert --to reachthe surge drum and changes the second processing unit charge liquidflowrate at approximately that time to minimize the effect of the change inthe second processing unit charge liquid flow rate-- Col. '4, line'ZS:af,ter "respectively" should be Col. 5, line 15: 'r'puositive" shouldread -positive Col. 5, line 61: "is" should read --in-- Signed andsealed this 3rd day of December 1974.

(SEAL) Attest:

McCOY 1:4. cnason JR. v I MARSHALL DANN Attestll'lg officerCommissionerof Patents

